Among the wide variety of known electronic displays, some involve electronically controlling the location of charged particles suspended in a fluid. Electrophoretic displays represent one type of electronic display and involve moving the charged particles suspended in the fluid with a Coulombic force exerted on the particles by an applied electrical signal. Some electronic displays are referred to as electronic paper or e-paper, since they can be thin and flexible with paper-like image quality. Electronic displays may use transmitted light, but some use only reflected light.
While a variety of technological approaches have been attempted, opportunities for improvement abound. For example, a challenge exists in producing a bright, full-color image in an electronic display using only reflected light. Unique conditions exist under which light is reflected and charged particles are moved about in a pixel of the display. As a result, technology borrowed from known electrophoretic fluids, such as liquid electrophoretic toner (LEP toner) used in offset printing, has not performed adequately in the electronic display application.
Known electrophoretic fluids may rely on providing a pigment capable of adsorbing a charge or may rely on a combination of a pigment encapsulated by a polymer to provide the charged particles. However, encapsulation is often done in situ during polymerization, where the pigment chemistry and polymer chemistry are interdependent, such that some polymers are only compatible with certain pigments. Also, pigment chemistry may be influential of particle charge, yielding particle charges that may vary between colors. Such incompatibilities and other problems give rise to a search for improved suspensions of charged colorant particles for which particle location can be electronically controlled. These suspensions may be referred to as electronic inks. Some electronic inks may be referred to as electrophoretic inks where the charged particles may be moved with a Coulombic force exerted on the particles by an applied electrical signal.